The essential goals of cardiopulmonary bypass (CPB) are to provide life support functions, a motionless and decompressed heart, and a bloodless field of view to facilitate cardiac surgery. CPB requires the use of cannulae to divert de-oxygenated blood from its normal circulatory path, through a heart-lung machine (i.e., a pump-oxygenator), and return oxygenated blood to the patient. This generally includes using both venous and arterial cannulae, and flushing the heart's coronary system with cardioplegia to arrest the heart. In a basic CPB system, oxygen-poor blood is drained by gravity or is siphoned from the patient's venous circulation and is transported to the heart-lung machine where carbon dioxide is removed from the blood and oxygen is added. The oxygenated blood is then returned or perfused into the patient's arterial circulation for distribution throughout the patient's entire body. This process requires a venous drainage cannula (or cannulae) to be placed into the right side of the heart (e.g. the right atrium), directly into the major veins (e.g. the superior vena cava (SVC) and/or the inferior vena cava (IVC)), or through peripheral vein access sites, to drain de-oxygenated blood from the patient and then deliver the blood to the heart-lung machine. Similarly, an arterial or aortic perfusion cannula is typically placed in the aorta or other large peripheral artery, such as the common femoral artery, to return or perfuse oxygenated blood to the patient. The patient's heart and lungs can thus effectively be bypassed, allowing surgeons to operate on a bloodless heart.
The venous cannula or cannulae are inserted usually directly through an incision in the right atrium or into the SVC and/or IVC for connection to the drainage side of the pump-oxygenator. Once the cannulae are in place and the connections are made to the heart-lung machine, CPB is instituted by allowing de-oxygenated blood returning to the right side of the heart to be diverted through the venous drainage cannula(e) and into the pump oxygenator where it is oxygenated and temperature-adjusted. From there, the blood is pumped into the patient's arterial system via the arterial or aortic perfusion cannula to provide oxygen-rich blood to the patient's body and brain.
If it is desired to drain or siphon blood from both the SVC and the IVC, two cannulae are typically used--one for each vena cava. This requires more work due to multiple incisions, multiple sutures, multiple connections to the heart-lung machine, etc., and may also obstruct the surgeon's view and the surgeon's access. To overcome these and other problems, it has been suggested that a single cannula be used, as shown, example, in U.S. Pat. No. 5,562,606 issued to Marinus, and U.S. Pat. No. 4,309,994 issued to Grunwald, both of which are expressly incorporated herein by reference. Marinus describes a cannula that is inserted through one of the vena cavae and extends through the right atrium into the other vena cava, wherein the cannula is provided with a cooling structure to help cool the right atrium. Grunwald describes a cannula that branches in two directions to allow drainage of both vena cavae, but requires the use of an obturator inserted therein to force the diverging branches together (e.g., for insertion or removal of the cannula through a trocar port). In addition, because the combined transverse cross-sectional areas of the two branches in Grunwald is less than the transverse cross-sectional area of the main cannula body from which the branches diverge, Grunwald appears to make inefficient use of the available drainage volume of the branches. Similarly, the drainage in Grunwald may be restricted due to possible kinks in the branches at the points where they diverge (referred to in Grunwald as the crotch).